This disclosure relates to a semiconductor switch device and to a method of making a semiconductor switch device.
Known RF (Radio Frequency) MOS (Metal-Oxide-Semiconductor) switches are based on a comb type layout. In this layout, the switch includes a gate that has a plurality of interconnected fingers. The fingers are interspersed with source and drain regions comprising elongate strips. Metal interconnects are provided to each source and drain region through a series of vias located at several points along each strip. Generally, the connection to the gate as made at one side of the device, at a common strip that interconnects each finger of the comb. The device may be surrounded by deep trench isolation (DTI). The DTI may be provided in the form of a mesh of trenches. This DTI implementation may generally increase the size of the device by a factor 2 or 3. Losses within such a switch may be relatively high. For instance, the isolation provided by the DTI surrounding the device does not affect substrate impedance within the device. The footprint of the active device itself may generally stay relatively wide and thus exhibit a lower substrate resistance, which may lead to higher insertion losses and a higher noise figure.
Scaling of such a device is also limited to adding additional fingers to the comb or by varying the length of the fingers.
Within a single-pole, single-throw (SPDT) switch there are several ways to provide electrostatic discharge (ESD) protection. One approach is to use ESD self-protected switches. In such an approach, only a first finger of the switch bears the ESD stress. The other fingers of the device do not participate in this respect because there is no domino effect in this kind of device. Because of this, the width of the first finger may be required to be relatively large, which may increase insertion losses and the noise figure of the device.